The invention relates to a process and apparatus for the removal of residues from equipment, particularly extruder screws, used in the polymerization and other processing of synthetic materials, such as plastics. More particularly, the invention is directed to the removal of residues by means of pyrolysis in a closed heating chamber provided with at least one exhaust vent for distilled gases.
After brief or extended periods of operation of equipment used in the polymerization and processing of plastics, for example extruder screws, high melting point and non-melting residues remain on the equipment, which residues interfere with production and must be regularly removed. The residues may be removed by brushing or chipping, by burning with liquid fuel, or by treatment in chemical baths. However, the known processes have considerable disadvantages. Thus, the action of cleaning by known processes is too vigorous and too irregular so that there is danger of damage to the surfaces as well as the shape and structure of extruder screws, which are often several meters long.
It is already known that equipment used for holding articles being lacquered may be cleaned by removal of the lacquer residues by means of pyrolysis, i.e., the heating of the equipment in the absence of air. German Pat. No. 1,220,299 issued Jan. 26, 1967 to Siemens A. G. describes such a process and apparatus, according to which the equipment is heated in the absence of air until the lacquer residues are completely burned up and distilled gases may be drawn off through a chimney. The extracting temperature is approximately 650.degree. C. To applicants' knowledge this known process has not yet been used for the handling and treatment of extruder screws.
The apparatus described in German Pat. No. 1,220,299 is improved upon in German Pat. No. 2,247,861 issued May 15, 1975 to Siemens A. G., by making use of the distilled gases to heat the heating chamber. In addition, German Patent Application No. 2,512,603 filed Mar. 21, 1975 by Siemens A. G. describes the introduction of an inert gas, such as nitrogen or carbon dioxide, into the heating chamber to reduce the risk of explosion and to obtain uniform burning.
In another known apparatus which can be used to clean extruder screws, the equipment to be cleaned is heated under vacuum, and the resulting distilled gases are exhausted.
It is the object of the present invention to create a process and apparatus of the type indicated, which are simpler and more economical as well as insuring extremely careful and effective treatment in the removal of residues from equipment being cleaned, particularly extruder screws.